Nickel-cobalt base alloys



nited rates atcnt 3,027,254 NICKEL-COBALT BASE ALLOYS Jerome BenedictMalerich, West Peabody, and Robert Francis Wilde, Lynnfield, Mass,assignors to General Electric Company, a corporation of New York NoDrawing. Filed Apr. 21, 1959, Ser. No. 807,780 3 Claims. (Cl. 75-171)This invention relates to nickel-cobalt base alloys suitable forcasting, particularly unique in improved elevated temperature ductilityand impact strength.

Designers of articles intended for use at elevated temperatures understress and vibratory conditions resist the use of materials having lowductility and poor resistance to impact. Unfortunately, the propertiesof many cast materials include such undesirable properties, yet theproduction costs of many articles manufactured by casting methods, suchas accurate vacuum investment casting methods, are considerably lowerthan other methods such as machining or forging.

Therefore a principal object of our invention is to provide a castingalloy having suitable strength characteristics for elevated temperatureapplications under stress conditions and including greater ductility andimpact strength properties than currently available cast alloys.

Another object is to provide a nickel-cobalt alloy ineluding a balanceof aluminum, titanium, carbon, mlybdenum and iron to provide ductilityin a casting usually found in wrought articles.

Our alloy in one form comprises in percent by weight about 0.10-0.16carbon, about 2-2.5 titanium, about 3.5-4 aluminum, about 4-5molybdenum, about 14-16 chromium, about 26-28 cobalt, up to about 2iron, about .01-.02 boron, with the balance essentially nickel,impurities, and the usual small quantities of manganese and silicon.However, we prefer that our alloy include in percent by weight a maximumof about 0.2 manganese and a maximum of about 0.3 silicon.

Our alloy features excellent ductility and impact strength principallyas a result of a balance between the alloying of titanium, aluminum,iron, molybdenum and carbon with a nickel-cobalt base includingchromium. We have found that the ductility and impact strength ismaintained at a superior level if the Al/Ti ratio is at about 2 orbelow, at the same time as the Ti/ C ratio is maintained at about 16 orbelow and the Mo/Fe ratio is about 2.5 or greater.

We prefer to refer to our alloy as a casting alloy because it displaysexcellent stress rupture strength inherent in castings over that ofwrought materials. For example, in the range of about A our alloyexhibits average 100 hours stress rupture life at 1350 F. of 68,000pounds per square inch, at 1500 F. of 46,000 pounds per square inch andat 1650 F. of 28,000 pounds per square inch. However our alloy has theductility for engineering applications generally only obtainable inwrought materials.

In order to determine the ductility, sometimes referred to as tensileductility, of our alloy in its broad range, we conducted a series oftensile tests from which may be calculated the ultimate tensilestrength, referred to in the tables as U.T.S., percent elongation andpercent reduction in area. Ultimate tensile strength" is the value inpounds per square inch obtained when the maximum load recorded duringthe straining of a specimen is divided by the cross sectional area ofthe specimen before straining. Tensile ductility is the measure of thepermanent deformation before fracture by stress when the specimen is intension. Percent elongation may be defined as the amount of permanentextension in the vicinity of the fracture during a tensile testexpressed as percentage of the originally gage length; the percentagereduction in area, shown as percent R.A. in the tables, may be definedas the percentage difference between the original cross sectional areaand that of the smallest area at the point of rupture of a testspecimen.

Table 1 represents average and maximum tensile data for a large numberof specimens tested having grains sizes up to about A Our alloy was castdirectly into the 0.250 inch diameter test specimens size and had agrain size range of about to inch. The gauge length of the testspecimens upon which the following elongation values were based was 1inch.

Table I U.1.S. (1,000 Elongation RA. (percent) p.s.i.) (percent) Temp.F.)

Avg. Max. Avg. Max. Avg. Max.

Another measure of ductility of an alloy is an impact test conducted todetermine the energy, usually measured in foot pounds, absorbed infracturing a test bar. The impact test which we used was a standardA.S.T.M. V notch Charpy impact test performed on a test bar cantileveredat both ends and including a notch in one face. The bar is impacted onthe side opposite the notch by a falling weight possessing a potentialenergy of about 117 foot pounds. We obtained the average data shown inTable II from alloys having the composition in percent by weight of0.10-0.16 carbon, 2-2.5 titanium, 3.5-4.0 aluminum, 4-5 molybdenum,14-16 chromium, 26-28 cobalt, a maximum each of 0.2 manganese and 0.3silicon, a maximum of 2 iron, 0.01-0.02 boron with the balanceessentially nickel and impurities (grain size= Table 11 Temp. F.):Impact force (foot pounds) Room Although a number of cast nickel basealloys have been reported as suitable for elevated temperatureapplications, we have found it to be desirable to maintain our Al/Tiratio at or below about 2 at the same time as our Ti/C ratio is at orbelow about 16 and our Mo/Fe ratio is at least at about 2.5 within therange of our alloy.

Table III compares these essential elements in some other cast alloys,the impact strengths of which we tested with our alloy.

Table IV gives the results of impact testing at 1500 F. using the CharpyV notch impact test (grain size==% Table IV Alloy: Impact force (footpounds) Our 12 -A 4 Although we have described our alloy in connection 73 with specific examples referring to grain size in a certain range andour alloy tested in the as-cast condition, it will be understood bythose familiar with the art of metallurgy and heat treatment thevariations and modifications of which our alloy is capable.

What we claim is:

1. A nickel-cobalt base cast alloy comprising in percent by weight about0.10-0.16 carbon, about 2-2.5 titanium, about 3.5-4.0 aluminum, about4-5 molybdenum, about 14-16 chromium, about 26-28 cobalt, up to about 2iron, about 0.01-0.02 boron, with the balance essentially nickel andimpurities and having an Al/ Ti ratio of about 2 or below, a Ti/ C ratioof about 16 or below and Mo/Fe of at least about 2.5.

2. An article cast from the alloy of claim 1 having a grain structure insize up to about A 3. A nickel-cobalt base cast alloy comprising in per-References Cited in the file of this patent UNITED STATES PATENTS2,688,536 Callaway et a1. Sept. 7, 1954 FOREIGN PATENTS 548,778 CanadaNov. 12, 1957 92,627 Norway Oct. 13, 1958

3. A NICKEL-COBALT BASE CAST ALLOY COMPRISING IN PERCENT BY WEIGHT ABOUT0.10-0.16 CARBON, ABOUT 2-2.5 TITANIUM, ABOUT 3.5-4.0 ALIMINUM ABOUT 4-5MOLYBDENUM, ABOUT 14-16 CHROMIUM, ABOUT 26-28 COBALT, UP TO ABOUT 2IRON, ABOUT 0.01-0.02 BORON, A MAXIMUM EACH OF ABOUT 0.2 MANGANESE ANDABOUT 0.3 SILICON WITH THE BALANCE ESSENTIALLY NICKEL AND IMPURITIES ANDHAVING AN AL/TI RATIO OF ABOUT 2 OR BELOW, A TI/C RATIO OF ABOUT 16 ORBELOW AND MO/FE RATIO OF AT LEAST ABOUT 2.5.